r- t — NPS-68-87-008 NAVAL POSTGRADUATE SCHOOL Monterey , California 7 THESIS THE PHYSICAL OCEANOGRAPHY OF THE NORTHERN BAFFIN BAY-NARES STRAIT REGION by Victor G. Addison, Jr. December 1987 Thesis Advisor R.H. Bourke Approved for public release; distribution is unlimited. Prepared for: Dierctor, Arctic Submarine Laboratory Naval Ocean Systems Center San Diego, CA 92152 T238665 NAVAL POSTGRADUATE SCHOOL Monterey, California Rear Admiral R. C. Austin Kneale T. Marshall Superintendent Acting Provost This thesis was prepared in conjunction with research sponsored by the Arctic Submarine Laboratory, Naval Ocean Systems Center, San Diego, California under Work Order N66001 - 86-WR-00131 . Reproduction of all or part of this report is authorized. ^classified REPORT DOCUMENTATION PAGE REPORT SECURITY CLASSlf.CATiON UNCLASSIFIED ID REST R.CTIV t MARKINGS security classification authority j distribution, availability of repori Approved for public release; distribution is unlimited. DECLASSifiCATlON/ DOWNGRADING SCHEDULE NPS 68-87-008 NAME OF PERFORMING ORGANIZATION Naval Postgraduate School 6d OFF'Ct SVMBOu (it appJfCatWe) Code 68 7a NAME Of MONITORING ORGANIZATION Arctic Submarine Laboratory ADDRESS (City, Sure, and ZIP Code) Monterey, CA 93943-5000 7d ADDRESS (City, State, and ZlPCodt) Code 19, Bldg. 371 Naval Ocean Systems Center San Diego, CA 9215? NAME 0*" F UNDiNG / SPONSORING ORGANIZATION Arctic Submarine Laboratorv 80 Off CE Symbo. (It ipphable) Code IP 9 PROCUREMENT INSTRUMENT IDE NTlf 1 CAT 1 ON NUMBER N66001 86VR00131 ADDRESS (C/r,. Stile, end ZiP LooeJ Bldg. 371 Naval Ocean Systems Center Sar. Diego, CA 92152 1 ,r ' SOuPC: C : -i IJ\>NG NUMB? 5 ' k PROGRAM ELEMENT no PROJECT NO TASK NO AO^. UNiT ACCESSION NO TiTit (inciuoe security Cussiticmon) THE PHYSICAL 0CEAN0CRAPHY OF THE NORTHERN BAFFIN BAY-NARES STRAIT REGION \ PERSONAL AUTHOR(S) Addision, Victor G., Jr. la TYPE O? REPORT 1 So Time covered 14 DATE OF REPORT (Ye*r, Month, D*y) 15 PAGE COUNT Master’s Thesis CROM TO 1987 December 110 > SUPPLEMENTARY NOTATION Prepared in conjunction with R.H. Bourke and R.G. Paquette COSATI CODES FIELD GROUP SUB-GROUP 16 SUBJECT TERMS (Continue on reverse i> necessity end identity py brock number) Baffin Bay Nares Strait SIR JOHN FRANKLIN North Water ) ABSTRACT (Continue on reverse it necessity tnd identity o y block numoer) A dense network of conductivity-temperature-depth (CTD) measurements was conducted from .affin Bay northward to 82 t ’09’N at the entrance to the Lincoln Sea, in most comprehensive hysical oceanographic survey ever performed in the northern Baffin Bav-Nares Strait (NBB-NS) egion. These data indicate Nares Strait Atlantic Intermediate Water (NSATW) and Arctic asin Polar Water (ABPW) to be derived from Arctic Basin waters via the Canadian Archipelago, 'hereas the West Greenland (WGC) is the source of the comparatively dilute West Greenland iurrent Atlantic Intermediate Water (WGCAIW) and West Greenland Current Polar Water (WGCPW) tactions. Baffin Bay Surface Water (BBSW) is found seasonally throughout northern Baffin iay. Recurvature of component branches of the WGC, which attains a maximum baroclinic ransport of 0.7 Sv, occurs primarily in Melville Bay (0.2 Sv) , south of the Carey Islands 0.1 Sv) and ultimately in Smith Sound (0.2 Sv). The Baffin Current originates as an ce-edge jet in Smith Sound and is augmented by net outflow from Smith, Jones, and Lancaster ounds at rates of 0.3 Sv, 0.3 Sv and 1.1 Sv, respectively. Circulation in Smith, Jones and o distribution/ availability of abstract OuNCLASStfiED/UNllMlTED □ SAME AS RPT Q OTIC USERS 2 1 ABSTRACT SECURITY CLASSIFICATION UNCLASSIFIED NAME O fc RESPONSIBLE INDIVIDUAL R,H. Bourke 2/ o TELEPHONE tinciude Arei Code) ( 408 ) 64t>-3270 OFFICE SYMBOL 68Bf FORM 1473, B4 mar 83 apk edition may De u*eo until emausteo Ail otner editions are ooso*ete SECURITY CLASSIFICATION Of this PAGE i u.s. «nl Pti'ii.M, 0"ic« 1 UNCLASSIFIED SECURITY CLASSIFICATION of THIS RAGE prh«n Dmtm Bnfr*4) Block 18 (continued) Geostrophic Estuarine Circulation Lancaster Sound Jones Sound Smith Sound Kane Basin Melville Bay Block 19 (continued) Lancaster Sounds can be described in terms of the Geostrophic Estuarine Circulation Model (GEC) . The North Water is caused by the combined influences of near-surface layer enthalpy and mechanical ice removal. S N 0102* LF- 014* 6601 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS RAGE(Tn>#n Dmtm Enfrmd) 2 Approved for public release; distribution is unlimited. The Physical Oceanography of the Northern Baffin Bay-Nares Strait Region by Victor G. Addison, Jr. Lieutenant, United States Navy B.S., State University of New York, Stony Brook, 1979 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN METEOROLOGY AND OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL December 1987 abstract ^ ) A dense network of conductivity-temperature-depth (CTD) measurements was conducted from Baffin Bay northward to 82’09'N at the entrance to the Lincoln Sea, in the most comprehensive physical oceanographic survey ever performed in the northern Baffin Bay-Nares Strait (NBB-NS ) region. These data indicate Nares Strait Atlantic Intermediate Water (NSAIW) and Arctic Basin Polar Water (ABPW) to be derived from Arctic Basin waters via the Canadian Archipelago, whereas the West Greenland Current (WGC) is the source of the comparatively dilute West Greenland Current Atlantic Intermediate Water (WGCAIW) and West Greenland Current Polar Water (WGCPW) fractions. Baffin Bay Surface Water (BBSW) is found seasonally throughout northern Baffin Bay. Recurvature of component branches of the WGC, which attains a maximum baroclimc transpoit of 0.7 Sv, occurs primarily in Melville Bay (0.2 Sv) , south of the Carey Islands (0.1 Sv) and ultimately in Smith Sound (0.2 Sv) . The Baffin Current originates as an ice-edge jet in Smith Sound and is augmented by net outflow from Smith, Jones, and Lancaster Sounds at rates of 0 . 3 Sv, 0.3 Sv and 1.1 Sv, respectively. Circulation in Smith, Jones and Lancaster Sounds can be described in terms of the Geostrophic Estuarine Circulation Model (GEC) . The North Water is caused by the combined influences of near-surface layer enthalpy and mechanical ice removal. 4 T> TABLE OF CONTENTS I . INTRODUCTION 12 A. PURPOSE 12 B. BACKGROUND 13 1. Bathymetry 15 2. General Circulation 16 3. Water Masses 19 4. The North Water 20 II. METHODS AND MEASUREMENTS 23 A. CRUISE SUMMARY 23 B. INSTRUMENTATION 23 C. DATA REDUCTION AND ANALYSIS 25 III. THERMOHALINE STRUCTURE 28 A. INTRODUCTION 28 B. BAFFIN BAY SURFACE WATER 28 C. POLAR WATER 34 D. ATLANTIC INTERMEDIATE WATER 53 IV. CIRCULATION AND TRANSPORT 58 A. INTRODUCTION 58 B. DYNAMIC TOPOGRAPHY 58 C. THE WEST GREENLAND CURRENT 61 D. CIRCULATION IN NARES STRAIT 65 E. THE BAFFIN CURRENT 70 F. CIRCULATION IN THE SOUNDS 71 1 . Introduction 71 5 2. Smith Sound 71 3 . Jones Sound 73 4. Lancaster Sound 75 5. Geostrophic Estuarine Circulation 75 G. BAROCLINIC TRANSPORTS 82 V. THE NORTH WATER PROCESS 88 VI. DISCUSSION 92 VII . CONCLUSIONS 94 APPENDIX: COMPUTATIONS ASSOCIATED WITH THE GEC MODEL 96 LIST OF REFERENCES 98 INITIAL DISTRIBUTION LIST 100 6 LIST OF TABLES I. NEAR-SURFACE AND INTERMEDIATE- DEPTH WATERS OF THE NORTHERN BAFFIN BAY-NARES STRAIT REGION 29 II. GEOSTROPHIC ESTUARINE CIRCULATION MODEL CALCULATIONS 79 7 LIST OF FIGURES 1.1 A chart of the northern Baffin Bay-Nares Strait region 14 1.2 The West Greenland Current and the Baffin Current (from Muench, 1971, p. 2) 17 1.3 The approximate monthly mean extent of the North Water (from Dunbar, 1970, P- 279) 21 2.1 The locations of CTD stations conducted during the September 1986 cruise of CCGS SIR JOHN FRANKLIN 24 2.2 The locations of transects used in the analysis 26 3.1 A composite temperature profile illustrating the shallow thermocline characteristic o t BBSW 31 3.2 The horizontal distribution of maximum temperatures in the BBSW layer 32 3.3 A T/S transect northeastward across Melville Bay 33 3.4 A meridional T/S transect from Baffin Bay northward to Kane Basin 35 3.5 A composite salinity profile illustrating the dilution of WGCPW relative to ABPW 37 3.6 A composite densitv profile illustrating the dilution of WGCPW reLative to ABPW 38 3.7 A composite T/S curve illustrating knee salinities characteristic of WGCPW and ABPW 39 3.8 A composite T/S curve illustrating the absence of a sharp knee in stations north of Smith Sound 41 3. g The horizontal distribution of ABPW and WGCPW in the NBB-NS region 42 3.10 A composite temperature profile illustrating the interleaving of ABPW and WGCPW in Smith Sound. Jones Sound and Melville Ba v 44 3.11 A T/S transect northward across Melville Bav 45 3.12 A T/S transect across Kane Basin 46 3.13 A T/S transect across the southern entrance to Kane Basin.... 48 8 3.14 A T/S transect across the mouth of Jones Sound 49 3.15 A T/S transect across the mouth of Lancaster Sound 50 3.16 A composite density profile illustrating the magnitude of glacial mel twater- induced stair-stepped layering in Kane Basin 51 3.17 A T/S transect in Robeson Channel 52 3.18 The horizontal distribution of NSAIW and WGCAIW in the NBB-NS region 54 3.19 A meridional T/S transect from Kane Basin northward through Kennedy and Robeson Channels 56 3.20 A T/S transect Jones Sound eastward to Thule 57 4.1 Surface circulation in the NBB-NS region 59 4.2 The surface dynamic topography referenced to 200 decibars, in dynamic centimeters 60 4.3 A baroclinic velocity cross section through Melville Bay 63 4.4 A baroclinic velocity cross section from Jones Sound eastward to Thule. 64 4.5 A meridional baroclinic velocity cross section from Baffin Bay northward to Kane Basin 66 4.6 A baroclinic velocity cross section through a southern part of Kennedy Channel 67 4.7 A baroclinic velocity cross section through Che southern portion of the Kane Basin Gyre 69 4.8 A baroclinic velocity cross section through Smith Sound 72 4.9 A baroclinic velocity cross section through Jones Sound 74 4.10 A baroclinic velocity cross section through Lancaster Sound.. 76 4.11 A schematic cross section of coastal upper layer flow (from Leblond, 1980, p. 191) 77 4.12 Surface dynamic height anomalies in Lancaster Sound (in dynamic cm) relative to 300 dbar level (from Fisse'l et al., 1982, p. 187) 80 4.13 Dvnamic topography of the surface relative to 500 dbars in Jones Sound for various years (from Mueneh. 19 7 L. p. 92) 8 3 9 4.14 Major baroclinic transports in the NBB-NS region .....85 5.1 Enthalpy of the near-surface (upper 75 m) layer in the NBB-NS region (referenced to 1.8°C) 90 10 ACKNOWLEDGEMENTS Funding for the work described in this thesis was provided by the Arctic Submarine Laboratory, Naval Ocean Systems Center, San Diego, California under Work Order N- 66001 - 86 -WR00131 . I wish to thank Dr. R.H. Bourke for initially providing me with the opportunity to participate in this study, and, thereafter, for his invaluable assistance and encouragement. Dr. R.G. Paquette is also gratefully acknowledged for his advice and assistance and, in particular, for this continued support during periods of severe personal hardship . The success of the cruise can be attributed to the enthusiasm and dedication of the Captain and crew of the CCGS SIR JOHN FRANKLIN. I also wish to thank A.M. Weigel, K.O. McCoy and Dr. P. Jones for their innumerable personal contributions to this effort. Miss J.E. Bennett is also gratefully acknowledged for her indispensable assistance in the preparation of this manuscript. Finally. I wish to thank my lovely wife, Karen, for being there when I needed her. 11 I. imQDVCTIQE A. PURPOSE During September 1986, the CCGS SIR JOHN FRANKLIN conducted an oceanographic measurement program from Baffin Bay northward into Nares Strait, to the southern reaches of the Lincoln Sea. This expedition marked the first comprehensive use of continuous profiling conduc tivi ty- temperature -depth (CTD) measurements throughout the region, and the northernmost transit (82°09'N) of a surface ship through Nares Strait since the 1971 voyage of the CCGS LOUIS S. ST. LAURENT. Sponsorship of this endeavor was provided by the Arctic Submarine Laboratory, with diplomatic concurrence from the governments of Canada and Denmark. The principal objective of the cruise was to examine the distribution of physical oceanographic variables from Baffin Bay northward, in order to determine the circulation and water mass characteristics of the region. The successful transit of the region by the SIR JOHN FRANKLIN provides a data set from which it is possible, essentially for the first time, to thoroughly define the baroclinic circulation and water mass structure of the northern Baffin Bay-Nares Strait region. Specific objectives of the analysis will be to: (1) define the trajectory, transport and extent of the West Greenland and Baffin Currents; (2) describe the charac teristics and extent of the water masses found throughout the region: (3) characterize the role of topographic steering and bathymetric boundaries on baroclinic 12 circulation and water mass penetration; (4) present a model which explains the observed circulation in Smith, Jones, and Lancaster Sounds; and (5) present a hypothesis for the formation and maintenance of the North Water, a large polynya located in Northern Baffin Bay. B . BACKGROUND The northern Baffin Bay-Nares Strait (hereinafter referred to as NBB-NS) region is historically significant for a number of seemingly unrelated reasons (Figure 1.1). Lancaster Sound, noted as the traditional Atlantic entrance to the Northwest Passage and as a net source of Arctic Ocean water inflow to the region, remains relatively ice free during winter. Indeed, northern Baffin Bay as a whole was thought to remain conspicuously unencumbered by ice during the winter due to the presence of the North Water. The Humboldt Glacier, the largest glacier in the northern hemisphere, is located on the eastern side of Nares Strait and is the source for many of the icebergs which are observed throughout the NBB-NS region. Once calved from the glacier, many of these icebergs travel southward past Cape York, in defiance of the northward flowing West Greenland Current. The most comprehensive oceanographic analysis of the northern Baffin Bay region is provided by Muench (1971). Muench's work serves as a summary of all significant oceanographic research conducted prior to 1971, and has been referenced in all subsequent analyses of the NBB-NS region. Prior to 1972, all baroclinic oceanographic analyses in the NBB-NS region were derived from bottle sampling techniques. The CCGS LOUIS S. ST. LAURENT obtained discrete measurements of temperature and salinity in Nares Strait during August 1971, reaching a latitude of 82°56'N 13 Figure 1.1 A chart of the northern Baffin Bay-Nares Strait region. Ice concentrations greater than 7/10 (during the FRANKLIN 86 cruise) are represented as shaded areas. 14 (Sadler, 1976). During 1972, scientific personnel aboard the LOUIS S. ST. LAURENT obtained the first winter oceanographic data from Davis Strait utilizing an in situ salinity/temperature/depth unit (STD) (Muench and Sadler, 1973). Transports through Nares Strait have been investigated by Sadler (1976), providing the most accurate current meter derived estimates of Lincoln Sea inflow to the region. In 1978 and 1979, the Eastern Arctic Marine Environment Studies (EAMES) program utilized current meters and CTD stations to investigate the southward flowing Baffin Current (Fissel et al . , 1982). Research concerning the processes leading to the formation of the North Water has most recently been conducted by Steffen and Ohmura (1983). 1. Bathymetry The bottom topography of the NBB-NS region is complex and, as such, has the potential to exert significant control over physical oceanographic processes. The influence of glaciers on all aspects of the morphology of this region is quite obvious. Northern Baffin Bay is fed by Lancaster and Jones Sounds to the west, and Smith Sound to the north. Shoaling to depths of less than 200 m occurs at some point in both Lancaster and Jones Sounds, effectively restricting deeper Arctic Ocean inflow. A sill which ranges in depth from 160 m to 200 m is present at the southern end of Kennedy Channel, providing similar constraints on Lincoln Sea inflow to the region. Similarly, shoaling to a depth of 230 m occurs at the Smith Sound entrance to Kane Basin. The deep, relatively flat central portion of northern Baffin Bay is punctuated in its eastern portion l»v i shallow *700 in) bank 15 located in Melville Bay. A deep (500 m to 900 m) channel passes offshore from Cape York, terminating northward in Smith Sound. To the west, the mouths of Jones and Lancaster Sounds reach depths of 700 m, but the bottom northeast of Devon Island shoals to less than 200 m approaching Smith Sound. 2. General Circulation The baroclinic circulation pattern in the NBB-NS region is dominated by the northward flowing West Greenland Current (WGC) and the southward flowing Baffin Current (Figure 1.2). Augmenting the transport of the Baffin Current are net outflows from Jones and Lancaster Sounds, coupled with southward flow through Nares Strait. The net baroclinic transport through northern Baffin Bay has been computed to be approximately 2.0 Sv (10 6 m 3 s _1 ) southward (Muench, 1971). Muench postulated that this transport is driven by a higher surface elevation in the Arctic Ocean relative to that in Baffin Bay, presumed to be a consequence of differing water structures in their respective upper 250 m layers. Bottom topography, predominantly northerly winds, and meltwater admixture are thought to play variable roles in the maintenance of a cyclonic circulation pattern in northern Baffin Bay. The WGC, a significantly barotropic current, may be enhanced baroclinically by near-shore low salinity wedges of meltwater. Alternately, the Baffin Current exhibits the increased baroclinic intensity characteristically found in western boundary currents. The westward turning of the WGC off Cape York, and the southward turning of Lancaster Sound outflow, are both influenced by topographic steering < Muench. 1 L, 71). 16 Figure 1.2 The West Greenland Current and the Baffin Current (from Muench, 1971, p. 2). 17 Circulation features in the NBB-NS region may be subject to seasonal variations. Lemon and Fissel (1982) noted a general winter weakening of near- surface baroclinic currents by a factor of two or more. The WGC , which transports northward only 10% of the baroclinic volume transported southward by the Baffin Current, is not always present during late summer (Muench, 1971). The directional components of some features of the surface and baroclinic flow fields are temporally variable. Muench stated that reversals of baroclinic flow have been observed in Smith and Jones Sounds, while reversals of surface flow have occurred in Smith Sound. Lancaster Sound, however, consistently provides net inflow to Baffin Bay on the order of twice that of Smith or Jones Sounds (Muench, 1971). Anticyclonic eddies (sometimes referred to as counter currents) have been reported near Bylot Island (Fissel et al . , 1982), while cyclonic eddies have been observed off Cape York (Muench, 1971). Current speeds in the NBB-NS region, although variable, are consistently greatest in magnitude near eastern Lancaster Sound. Fissel et al . (1982), using current meters, found near-surface velocities of 0.75 m/sec in the portion of the Baffin Current located east of Lancaster Sound. Directly measured current speeds in Nares Strait are extremely variable in magnitude, with maximum near-surface values ranging from 0.1 to 0.60 m/sec (Sadler, 1976). Maximum baroclinic velocities in the WGC are on the order of 0.1 m/sec (Muench, 1971). The nature and vertical extent of the flow regimes in the NBB-NS region are spatially complex. Although the vertical extent of volume flow in the WGC probably reaches a depth ot 500 m. most 18 baroclinic flow is limited to the upper 100 m (Muench, 1971). The Baffin Current nominally extends to a depth of 500 m, with flow reaching the bottom (700 m to 840 m deep) in the region of its intrusion into Lancaster Sound (Fissel et al . , 1982). Significant baroclinic flow in this current is associated with the upper few hundred meters (Muench, 1971). The flow in Nares Strait has a substantial baroclinic component which reaches to depths of 300 m (Sadler, 1976). 3. Water Masses Adopting the usual convention for Arctic regions, Muench (1971) divided the waters of northern Baffin Bay into three layers: a cold (<0°C) upper Arctic Water layer; a warmer (>0°C) intermediate -depth Atlantic Water layer; and a cold (<0°C) Deep Water Layer. The Arctic Water, confined to the upper 200 m to 300 m, has an upper limit in salinity of approximately 34.0. The Atlantic Water extends from the bottom of the Arctic Water layer to depths of 700 m in Lancaster Sound and 1300 m in northern Baffin Bay, exhibiting salinities of 34.2 to 34.5. Baffin Bay Deep Water extends from the bottom of the Atlantic Layer to the seabed, and is characteristically isohaline at 34.48. The density of water masses in the NBB-NS region, as in other Arctic regions, is primarily determined by salinity. Surface and near- surface layers, therefore, are usually characterized by strong haloclines and associated pycnoclines. The delineation of a surface (upper 75 m) layer of Arctic Water, which is modified by boundary layer processes, has been suggested by Fissel et al. (1982). Since diverse processes such as solar heating, meltwater admixture, and wind mixing 19 play roles in the formation of this layer, its temperature and salinity characteristics vary seasonally. The thermohaline characteristics of the water masses of the region can generally be traced to their sources, while their horizontal extent is often determined by bathymetric effects. Arctic Water is water of Arctic Ocean origin which either entered Baffin Bay via Davis Strait and was modified by cooling and admixture of runoff within northern Baffin Bay, or was modified by cooling and freshening within the Arctic Ocean prior to entering Baffin Bay from the north. Mixing of inflowing Arctic Ocean Water and resident Baffin Bay Arctic Water of the same density occurs in southern Smith Sound, Jones Sound, and Lancaster Sound. Shallow sills present in Lancaster Sound, Jones Sound and Kennedy Channel prevent southward flow of Arctic Ocean Atlantic Water into Baffin Bay. Atlantic Water in northern Baffin Bay, therefore, originates from the Atlantic Ocean via Davis Strait (Muench, 1971). 4. The North Water Extensive interest has been focused on a persistent polynya , termed the North Water, which is located in northern Baffin Bay (Figure 1.3). Dunbar (1970) concluded that the polynya is defined by a stable northern boundary at the Smith Sound entrance to Kane Basin, and a consistent western ice edge which forms along Ellesmere Island. The locations of the eastern and southern boundaries are seasonally dependent. Significant penetration of the North Water occurs westward into Lancaster Sound in June. The phenomenon is less well defined during the summer season after ice break up commences. Contrary to earlier reports, the North Water region is not completely open during 20 Figure 1.3 The approximate mean monthly extent of the North Water in: March (...), April ( ), May ( — ), June ( ); (from Dunbar. 1970, p. 279). 21 winter, and is characterized by extensive areas of new ice formation (Dunbar, 1973). Steffen and Ohmura (1985) used thermal infrared measurements from an airplane in winter to determine that the North Water was mostly covered with new and young ice, and probably devoid of first year ice until March. The ice surface, they surmised, was approximately 20°C warmer than that of the surrounding fast ice. The North Water essentially remains an unexplained phenomenon. Muench (1971) computed a heat budget for the region and concluded that insufficient heat is present in the Atlantic Water layer in northern Baffin Bay to prevent ice formation. He similarly concluded that there was not enough heat present in the surface Arctic Water layer either, and postulated mechanical ice removal by northerly winds and currents as the effects responsible for the formation of the North Water. Dunbar (1973) reinforced this hypothesis by noting that the age and thickness of ice increases from the Smith Sound ice arch southward. Steffen and Ohmura (1985), however, computed more accurate heat budgets for the region and concluded that oceanic heat of unknown origin is responsible for the formation and maintenance of this polynya . 22 II. METHODS AND MEASUREMENTS A. CRUISE SUMMARY Between 7 and 27 September 1986, the CCGS SIR JOHN FRANKLIN conducted the most extensive physical oceanographic survey ever performed in the NBB-NS region. The SIR JOHN FRANKLIN covered over 4000 km in the course of conducting 145 CTD stations (Figure 2.1; refer to Figure 2.2 for station number identification). Numerous transects were performed while transiting from Lancaster Sound northward to Robeson Channel, and subsequently southward to Melville Bay. Ice reconnaissance was provided by the SIR JOHN FRANKLIN's embarked helicopter, which was instrumental in enabling the ship to penetrate Robeson Channel to 82°09'N; the furthest northward of any ice breaker since 1972. B. INSTRUMENTATION The instruments used were the Applied Micro Systems Limited Conductivi ty -Temperature - Depth recorder, model STD- 12. This instrument has a stated accuracy of 0.02 mS/cm in electrical conductivity, 0.01°C in temperature and no stated accuracy in depth. The resolutions were stated to be 0.003 mS/cm, 0.001°C, and 0.05 dbar , respectively. Three instruments, numbered 422, 433 and 467, respectively, were utilized during the cruise. CTD //433 is the property of the Naval Postgraduate School (NPS), and was calibrated both before and after the cruise with resultant errors of 0.003°C in temperature and 0.007 mS/cm in conductivity. Calibrations for the other two instruments were not initially available, and were obtained empirically in the form of first 23 gure 2.1 The locations of CTD stations conducted during the September 1986 cruise of CCGS SIR JOHN FRANKLIN. degree polynomials by intercomparison with CTD #433 during simultaneous lowerings. It is concluded that the absolute error in the variables issmaller than 0.02°C, 0.02 mS/cm, and 2.0 dbars . The root mean square error in salinity, therefore, is approximately 0.03. The data were recorded internally in coded binary form, and were downloaded into a Compaq computer for conversion into engineering units and storage on 5.25 in. floppy diskettes. Each CTD was programmed to sample the data stream every 0.8 dbar of pressure change. Significantly finer resolution in pressure was not convenient because of computer memory limitations and downloading time constraints. The primary navigation aid was the ship's Magnavox MX 1107 Satellite Navigation System. An average of two fixes per hour provided a mean navigational accuracy of 0.5 km. C. DATA REDUCTION AND ANALYSIS Upon completion of the cruise, the data were transferred to mass storage cartridges for further processing with the NPS IBM 3033 computer. Editing of spurious and mis - sequenced data points, the cause of which is discussed by Tunnicliffe (1985), was subsequently performed. Removal of dynamic response errors in temperature and salinity was accomplished as prescribed by Bourke et al . (1986). The edited profile data were then sub-sampled every 5 m for use in the production of baroclinic velocity profiles and related volume transport estimates. Transects used in the data analysis for the construction of vertical sections are depicted in Figure 2.2. Temperature -salinity (T/S) transects are oriented as noted, with temperature values (°C) represented as solid lines and salinity values (Practical Salinity 25 Figure 2.2 The locations of transects used in the analysis. The dotted line denotes stations used for construction of meridional cross sections. 26 Scale) represented as dashed lines. Baroclinic velocity cross sections are oriented with velocities (cm /sec) "into" and "out of" the page represented as solid (positive values) and dashed (negative values), respectively . Surface dynamic heights and baroclinic velocity profiles were derived from the geostrophic approximation, assuming a level of no motion of 200 dbars . The technique of Helland -Hansen (1934) was deemed inappropriate for use in the NBB-NS region because of the inherently shallow and irregular bathymetry, thereby precluding the selection of a deeper reference level for regional application. Although a 200 dbar reference level is suitable for estimating direction in near-surface baroclinic currents, magnitudes were found to be underestimated by as much as 25% when compared to those derived with a level of no motion of 400 dbars . Baroclinic volume transports were calculated using variable reference levels, determined by the maximum common sample depth in a station pair. As the sample depths were occasionally limited by mechanical rather than bathymetric considerations, the associated transports may be subject to underestimation accordingly. The transports were calculated by vertical trapezoidal integration of baroclinic velocities over 5 m intervals. 27 III. THERMOHALINE STRUCTURE A. INTRODUCTION In order to more accurately characterize the near-surface and intermediate depth waters of the NBB-NS region, a delineation of five discrete water masses by vertical distribution of temperature and salinity is required (Table I). Baffin Bay Surface Water (BBSW) is derived locally and found seasonally in northern Baffin Bay at depths of up to 75 m. It is present in both the Baffin Current and the WGC . In general, the water masses which uniquely comprise the WGC are found to be less saline than their counterparts which enter the NBB-NS region through the Canadian Archipelago. Although the salinity difference between the Polar Water fractions is small, it is useful as a classification tool. Mixing of Arctic Basin Polar Water (ABPW) and West Greenland Current Polar Water (WGCPW) should be expected to occur along isopycnal surfaces in regions where their domains overlap. Although the salinity distributions of Nares Strait Atlantic Intermediate Water (NSAIW) and West Greenland Current Atlantic Intermediate Water (WGCAIW) do not intersect, it is bathymetry which prevents mixing of these two source fractions. B. BAFFIN BAY SURFACE WATER Baffin Bay Surface Water (BBSW) is locally derived from the combined effects of meltwater admixture and solar heating. The large, ubiquitous glaciers in the NBB-NS region serve as a continuous source of meltwater during periods of insolation. Admixture of glacial runoff with Baffin Bay Polar Water (BBPW) creates a significant halooline and resultant pycnocline in the upper 50 m to 75 m of the water column. Concurrently, 28 TABLE I NEAR-SURFACE AND INTERMEDIATE DEPTH WATERS OF THE NORTHERN BAFFIN BAY-NARES STRAIT REGION >> <4- -O “O -Q O a; • 03 c — t— “O £ 03 03 <U O CD M- r— c 4-> 03 <u cd 4-> •f— ^ 4-> < T? i-H a> <4- 00 a; <2S O - - jQ >> >> r— “O CD -Q r—-a <D iH O r- L- to >>— ' 4-> “O A3 03 CO <D C A3 •r- r— C to C •r- CD U. 03 03 -O •r- CD ro J C <4- 00 < >> O <D LO S- 2 CD O Q_ *0 CD O “O •r- A3 to iH £= “O L- O a; >> — L. A3 0) O O L. a; 4-> L. C 4-> C to L. -O O 03 03 03 03 <u a> c U J *1 CD 4-> 03 a) CD 03 CL> C CD O 00 <U O 3 5 -o <u •*- 03 h- O A3 to s- C 1— 0 z ra 0 CVJ L- 05 J* u O O LU <4- O 3 00 03 03 0 3E 00 CD r- CD 00 r- 3 -O 21 3 >> CO < O 03 1 03 • c O 00 -O CO CL < h- .c < 03 O • • ♦ • • E 00 0 LO CO 0 M ♦ • * 0 h“ CO CO LO 00 00 CO CO CO HH E 1 Od 00 E 00 1 CVJ 1 1 LU 0 • O • 0 • 0 E I— O CVJ LO O r}- LO LO 0 <3* ^ 0 LO O OCON O CO • cvj 0 CO ♦ 0 • 0 < CO CO «Cf- LO Od A v V V V CO V V V CO A CO CVJ c z 0 hooo h- 00 a> 0 h- 00 <u hooo <D a; c c 00 00 3 1 1 00 h- h- CO CO - - 3 L- <D <D <: 4-> 4-> 4-> 00 03 03 c 0 Z 3 3 a; •r- w 4-> a) L. 3 C L. u 03 3 Cl 03 <U 03 r— 0 O r- 4-> 4— O CD 4-> 03 U CL ■0 3 C 3 3 c — 00 C 03 4-> a) •f— r— 4-> 00 >> to C <D 03 03 00 03 03 <d 4-> L. < CO CO <D 03 4-> -O z U 3 00 <u c O — O E Od •r* 3 t- to s- LU <4- 4-> Q_ 4-> 03 a> <d h- <4— O CO to t— S- 4-> < 03 <C a> O 03 C 3 CO • < — - 3 » CL Z H-. 29 •West Greenland Current T: > 0°C ‘Generally warmer than NSAIW Atlantic Intermediate S: 33.8 - 34.5 Water (WGCAIW) D: 250 m - 800 m the effects of solar heating are essentially confined to this surface layer due to its inherent buoyancy. The admittedly arbitrary delineation of BBSW by the 0°C isotherm serves to distinguish it from BBPW, rather than imply that the effects of insolation are restricted to a discrete temperature range. BBSW is best identified, however, by the presence of a strong, shallow thermocline (Figure 3.1). A seasonal reversal of the processes which create BBSW, ultimately results in its elimination. The distribution of BBSW is a regional phenomenon. The horizontal distribution of maximum temperatures in the BBSW layer shows distinct gradients in the meridional and offshore directions (Figure 3.2). This result implies that BBSW is formed primarily by coastal processes, and is subsequently advected throughout most of northern Baffin Bay. The complete absence of BBSW north of Smith Sound is due to the widespread occurrence of pack ice, which serves to raise the albedo of the region and reduce insolation. The considerable concentration of BBSW located in the shelf waters of Melville Bay contributes significantly to the baroclinici ty of the WGC . A qualitative examination of a T/S transect through Melville Bay not only indicates that a major portion of the baroclinicity occurs in the upper 100 m, but that the isohalines (isopycnals) related to the presence of BBSW assume a negative slope in the core of the WGC between Stations 122 and 123 (Figure 3.3). The seasonal presence of BBSW, therefore, would be expected to enhance the baroclinic transport of the WGC. 30 o rsi i o o o o o o oo o o o n o □ □ o o LD (W) Hld30 O • _ r\) i o o o CD 31 Figure 3.1 A composite temperature profile illustrating the shallow thermocline characteristic of BBSW. Refer to Figure 2.2 for station location. Figure 3.2 The horizontal distribution of maximum temperatures in the BBSW layer. 32 33 DISTANCE (Km) Figure 3.3 A T/S transect northeastward across Melville Bay. Temperature contours are indicated by solid lines and salinity contours by dashed lines. The presence of BBSW at an ice edge can be considered to represent an equilibrium state. The northernmost extent of BBSW is precisely correlated with the location of the pack ice edge. A meridional T/S transect from Baffin Bay northward to Kane Basin graphically illustrates this interaction between relatively warm surface water and an ice edge (Figure 3.4). A filament of BBSW dives subsurface between Stations 44 and 47 beneath water of lower density at the ice edge. An equilibrium state can exist if sufficient thermal advection is present to prevent ice growth. Mitigation of thermal advection or atmospheric cooling will cause the ice edge to advance or retreat, respectively. C. POLAR WATER Polar Water in the NBB-NS region is derived from two distinct sources. Direct inflow from the Arctic Ocean through the Canadian Archipelago is generically classified as Arctic Basin Polar Water (ABPW), whereas northward flow via the WGC through Davis Strait is termed West Greenland Current Polar Water (WGCPW) . Subtle contrasts in the thermohaline signatures of these two water masses are indicative of their different origins, and serve as qualitative tracers of their respective flow fields. Although both forms of Polar Water have origins in the Arctic Ocean, the flow of WGCPW follows a circuitous route around the southern tip of Greenland before entering the NBB-NS region. The cumulative influence of shelf and surf ace -dr iven processes on the thermohaline structure of WGCPW is, therefore, of greater magnitude than the effect of similar processes on ABPW. The primary modification which occurs is due to meltwater admixture, resulting in a net dilution of the water column. 34 irr fpr.r STA NO 22 28 32 41 44 147 <<•>) HldX 35 Figure 3.U A meridional T/S transect from Baffin Bay northward to Kane Basin. Viewed simpl is tically , WGCPW can be considered a diluted form of ABPW . The comparative decrease in salinity and, hence, density of WGCPW below the surface layer is most apparent in vertical property profiles (Figures 3.5 and 3.6). The maximum salinity of WGCPW is approximately 34.2, while ABPW reaches 34.8. The presence of Polar Water with an underlying warm layer produces a characteristic inflection, or knee, when temperature is plotted against salinity. This knee can be viewed as a boundary between the bottom of the arctic halocline, formed as a consequence of convective overturn in winter, and a deeper thermocline, which marks the transition to an underlying warm layer. The salinity and depth at which this knee occurs are functions of the inherent thermohaline characteristics of the particular Polar Water mass. The combination of relatively dilute WGCPW and underlying Atlantic Intermediate Water results in a knee with a salinity of 33.4 to 33.5, at depths ranging typically from 50 m to 120 m. As ABPW enters the NBB-NS region through Lancaster Sound, for instance, it is subject to interleaving and mixing along isopycnal surfaces. This comparatively undiluted inflow is characteristically more dense than the resident Polar Water of northern Baffin Bay, and consequently sinks. The resultant combination of comparatively saline ABPW and underlying Atlantic Intermediate Water produces a knee with salinities between 33.5 and 33.7, at depths of up to 250 m. A composite T/S curve illustrates the contrasting knee salinity ranges of WGCPW and ABPW (Figure 3.7). A reduction in significant insolation in the near -surface laver. or the absence an underlying warm laver. will result in a weaker thermal 36 o o o o o CO o o to o o o o in CD o CD (W) HId30 37 Figure 3.5 A composite salinity profile illustrating the dilution of WGCPW (Stations 122 and 140) relative to ABPW (Stations 6 and 87). o o o o o o o o o o o o o o oo CO in CD (N) Hld3Q 38 Figure 3.6 A composite density profile illustrating the dilution of WGCPW (Stations 122 and 140) relative to ABPW (Stations 6 and 87). o >-• h-* CH oo PO (3) 3UrUUy3dU3I 39 Figure 3.7 A composite T/S curve illustrating knee salinities characteristic of WO’CFW (Stations 138 and 142), an ABPW (Stations 4 and 6). gradient and a bend, rather than a sharply defined knee, in the curve. This condition is apparent north of Smith Sound due to the widespread occurrence of pack ice, with an associated increase in albedo (Figure 3.8). The thermohaline characteristics of the two Polar Water masses can be used to roughly estimate the horizontal extent of their flow regimes. A plan view of Polar Water distributions indicates that inflow of WGCPW represents the minority fraction of Polar Water in the NBB-NS region (Figure 3.9). WGCPW is prevalent along the West Coast of Greenland northward to Cape York, where a bifurcation in flow creates one filament which extends to Smith Sound and another which projects westward into Jones Sound. Northward passage of WGCPW into Kane Basin was not observed. ABPW is present from the Lincoln Sea to the southern end of Kane Basin, and throughout the central and western portions of Baffin Bay. The presence of ABPW at stations north of 77°N not only suggests that Smith Sound is a mixing site for the two Polar Water masses, but is indicative of southward passage of ABPW from Nares Strait into northern Baffin Bay. Inflow of ABPW is restricted to the southernmost portion of Jones Sound, implying significant mixing there as well. Inflow of ABPW to the region is greatest in Lancaster Sound, as indicated by the consistently high knee salinities encountered there. A filament of ABPW can be seen in the southwestern corner of Melville Bay at Stations 132 and 133, which marks the location of a frontal boundary between an extreme northeastern branch of the Baffin Current, possibly derived from Lancaster Sound outflow, and a southward flowing branch of the WGC . The 40 o (f) o oj n n 13 LO CD CD CD 0 OGOO ♦ — i f— I ^ 1 « I I CO o < + X I o CM ■ LO ro m ro o ■ TT* ro ■ ro ro ■ ro ro LO o o i o CM >H h- • CM ro . CO • CM ro LO ro o ro LO h- o ro o . ro (0) 3ynibb3dU3I 41 Figure 3.8 A composite T/S curve illustrating the absence of sharp knee in stations north of Smith Sound. Figure 3.9 The horizontal distribution of ABPW and WGCPW in the NBB-NS region. 42 extensive interleaving which would be expected in regions such as these, where ABPW and WGCPW coexist, is evident in composite temperature profiles (Figure 3.10). The presence of subsurface temperature extremes in the Polar Water layer is associated with the contrasting effects of convective overturn in winter and insolation in summer. Convective overturn during ice formation creates a cold, isohaline layer which can project to a depth of greater than 50 m locally. Lateral infusion of brine produced during the freezing of shelf waters can increase the vertical extent of this isohaline layer to over 100 m. Subsequent surface heating and meltwater mixture produces significant enthalpy increases in the shallow pycnocline layer only, isolating an underlying cold lens at depths typically between 50 m and 150 m. South of Smith Sound cold lenses are sharply defined by strong temperature gradients. This is typically the case in Melville Bay, where cold, isohaline water is sandwiched between an overlying layer of BBSW and an underlying layer of Atlantic Intermediate Water (Figure 3.11). The absence of cold lenses north of Smith Sound is indicative of the inherently persistent ice cover. The associated high albedo results in steadily decreasing temperatures towards the surface and, consequently, no subsurface cold lenses are apparent north of Station 72, located at approximately 79.2°N (Figure 3.12). Southward decreases in ice concentration result in the formation of diffuse cold lenses in northern Smith Sound. A T/S transect taken at the southern entrance to Kane Basin reveals the remnants of a subsurface 43 o rsj cun HIcGO 44 Figure 3.10 A composite temperature profile illustrating the interleaving of ABPW and WGCPW in Smith Sound (Station 42), Jones Sound (Station 16), and Melville Bay (Station 133) . 45 Figure 3.11 A T/S transect northward across Melville Bay. ON Vl$ MN O O O co O o (*) o o U5 Hld30 o o CD o o o 46 Figure 3.12 A T/S transect across Kane Basin. Note the absence of a subsurface cold lens . cold lens on the western side, and alternating warm and cold layers to the east (Figure 3.13). Pronounced warm lenses are located on the southern side of Lancaster Sound, and along both boundaries of Jones Sound. Conditions in Jones Sound, with ambient air temperatures averaging -4°C and the presence of new ice observed along both shores, indicate that the local occurrence of subsurface lenses of BBSW is due to the initiation of convective overturn (Figure 3.14). The warm lens in southern Lancaster Sound is a sharply defined feature located at a depth of approximately 10(> m (Figure 3.15). The depth of this warm lens indicates that it is probably an outflow jet of ABPW which dives subsurface upon encountering a cooler, but comparatively less saline layer of resident Polar Water. This effect further illustrates the point that ABPW is more saline than the residual Polar Water mixture of northern Baffin Bay, and is subject to mixing along isopycnals at deeper depths. The major source of meltwater in the NBB-NS region is the Humboldt Glacier, located on the eastern side of Kane Basin. All stations in Kane Basin south of approximately 79°56'N (Station 84) have low surface salinities, typically approaching 31.0, and exhibit significant stair- stepped layering in vertical density structure (Figure 3.16). This not only illustrates the magnitude of glacial influence in the region, but suggests that extensive recirculation of near-surface waters may occur in Kane Basin. A significant local source of meltwater is apparent in the northwest corner of Robeson Channel, where surface salinities were generally below 30.0, the lowest encountered in the NBB-NS region (Figure 3.17). 47 DEPTH (m) NW STA NO 55 56 57 58 59 SE Figure 3.13 A T/S transect across the southern entrance to Kane Basin. Note the remnant of a cold lens at Station 55, and alternating warm and cold layers to the east . 48 S STA. NO. 13 14 15 16 N Figure 3.14 A T/S transect across the mouth of Jones Sound. 49 DEPTH (m) S STA. NO. I 2 3 4 5 6 7 8 N Figure 3.15 A T/S transect across the mouth of Lancaster Sound . 50 o o o o o r\] o o ro o o o o in o o CD t W) Hld30 51 Figure 3.16 A composite density profile illustrating the magnitude of glacial meltwater-induced stair-stepped layering in Kane Bn sin. S STA. NO. 105 103 99 N Figure 3.17 A T/S transect in Robeson Channel. 52 D. ATLANTIC INTERMEDIATE WATER The two Atlantic Intermediate Water fractions found in the NBB-NS region exhibit inherently different salinity characteristics and exclusive horizontal distributions. Nares Strait Atlantic Intermediate Water (NSAIW) is derived from the Atlantic Layer of the Arctic Basin and flows southward from the Lincoln Sea into Nares Strait. West Greenland Current Atlantic Intermediate Water (WGCAIW) flows northward through eastern Davis Strait, advected by the WGC into northern Baffin Bay . WGCAIW is warmer but less saline than NSAIW. Following the same line of reasoning which requires subdivision of the Polar Water fractions, WGCAIW is subject to more significant dilution effects by shelf and surf ace -dr iven processes compared to direct inflow from the Arctic Basin. Since CTD cast depths were not deep enough to reach the bottom of the WGCAIW layer, the upper limit in salinity presented in Table I for this water mass should be considered an estimate. The maximum salinity encountered in WGCAIW was 34. 44, at a depth of 562 m (Station 124), whereas a maximum salinity of 35.24 was recorded for NSAIW at a depth of 481 in (station 97). The comparatively lower temperatures in NSAIW are a reflection of the general north- south temperature gradient in the region. The highest Atlantic Layer temperature recorded in NSAIW was 0.20°C at a depth of 715 m (Station 95), in contrast with a maximum temperature of 1.81°C, recorded at a depth of 445 m (Station 133) for WGCAIW. The horizontal distributions of NSAIW and WGCAIW in the NBB-NS region are primarily determined by topographic ini iuences (Figure 3.18). 53 z Figure 3.18 The horizontal distribution of NSAIW and WGCAIW in the NBB-NS region. 54 Southward passage of NSAIW into Kane Basin is prevented by shoaling of the sea floor in southern Kennedy Channel (Figure 3.19). Although the major portion of WGCAIW flow is turned cyclonically to the southwest by the coastlines of Melville Bay and Cape York, northward transport of the remainder is abruptly terminated by a shallow bank (200 m) located in the vicinity of the Carey Islands. Northward flow of WGCAIW could continue to follow a deep narrow channel around this bank (Figure 3.20). but was not observed to do so. Once turned to the southwest, the flow of WGCAIW throughout northern Baffin Bay is not restricted by bathymetry. It should be noted that even with the hypothetical occurrence of westward flow from Cape York, penetration into Jones Sound by WGCAIW would be impossible because of shallow banks located east of the mouth. The flow into Lancaster Sound, however, is not similarly restricted. It is apparent that southeastern Lancaster Sound is a site of significant interleaving of dissimilar water masses, as the associated T/S cross section reveals the presence of BBSW, ABPW, and WGCAIW in profile (refer to Figure 3.15). It is presumed that WGCAIW is present at stations 7, 8, 9, 10 and 11, although the shallow CTD casts at these stations precludes absolute confirmation. 55 T3 '+-4 3 O w c aQ 0 / O 4-1 u 0 / w 00 H c c T3 CL < OC 56 through Kennedy and Robeson Channels. The meridional Cl Oy O 4-J 0) T 5 i-l ft >. 3 -O ^ -c r: 0 / C — i "O W-l C w 3 "O C w CO ^2 V) -H O <C c: ^ o f o - 3 S W4 o c l~i 3 O U Cm 0 / W 0 J cc H 00 0 / \ ^ H 2 ° < H O O rvj oC U 57 isotherm) is confined to a narrow channel. IV. CIRCULATION AND TRANSPORT A. INTRODUCTION Macroscale circulation in the NBB-NS region is dominated by the northward flowing WGC and the southward flowing Baffin Current. Although net southward flow in the region is maintained primarily by baroclinic forcing (Muench, 1971), bathymetry exerts considerable influence on the formation of mesoscale circulation patterns. An examination of the surface circulation of the region, as deduced from baroclinic velocity and dynamic height calculations, reveals the natuie of this influence (Figure 4.1). Reference to this surface circulation diagram is implied in the ensuing discussions. B. DYNAMIC TOPOGRAPHY An examination of the surface dynamic topography of the NBB-NS region referenced to 200 dbars indicates a general westward increase in dynamic heights (Figure 4.2). This trend is associated with the influence of the Coriolis force on the net southward flow. The shoreward gradient of the dynamic height contours, in northern Baffin Bay lends a cyclonic appearance to the circulation pattern. Meltwater runoff may be responsible for the increase in dynamic heights along the coastline of Melville Bay. The complex circulation patterns associated with the WGC are inferred from the reversal of gradients and bending of contours in the vicinity of Cape York. Northwestward flow around Cape York is diverted cyclonicallv to the south in the vicinity of the Carey Islands, an event associated with the limitation of northward flow of WGCAIW in the region :onthw<ud ( lowing branch of the WGC is clearly evident in Melville Bay. The flow reversal occurs on 58 Figure 4.1 Surface circulation in the NBB-NS region as deduced from baroclinic velocity and dynamic height calculations. 59 Figure 4.2 The surface dynamic topography referenced to 200 decibars, in dynamic centimeters. 60 the perimeter of a shallow bank, suggesting a possible topographic influence. Westward intrusions of surface flow are apparent at the northern sides of the entrances to both Lancaster and Jones Sounds. Although net flow is eastward in both cases, the closer spacing of contours in Lancaster Sound is associated with much greater baroclinic velocities. A significant portion of the ABPW outflow from Jones Sound into northern Baffin Bay is turned anticyclonical ly around the southeast shore of Devon Island, augmenting the westward intrusion of flow into Lancaster Sound. The sharp bending of contours in Smith Sound marks the boundary between two intersecting circulation regimes. A northward flowing branch of the WGC turns cyclonical ly , coincident with the formation of an ice-edge jet at the southern limit of the ice pack. The 0.36 dynamic meter contour is representative of the impingement of the relatively warm surface current on the ice pack, with a resultant density gradient normal to the ice edge. The deflection of southward flow from Nares Strait at the front is also apparent, but determination of associated circulation patterns within Kane Basin is not possible at this resolution. The meandering 0.28 dynamic meter contour in Kane Basin, however, is suggestive of the potential for gyre formation in this region . C. THE WEST GREENLAND CURRENT Circulation of the WGC in northern Baffin Bay appears to be governed by conservation of potential vorticitv. As a typical eastern boundary current, the WGC mav be assumed t o hrv a substantial barotropic component of flow. Conservation oi potential vorticity 61 requires barotropic flow to follow lines of constant f/H, where f is the Coriolis parameter, and H is the water depth. Since mesoscale variations in the Coriolis parameter can be considered negligible, flow will tend to parallel isobaths. Justification of the preceeding assumptions in the case of the WCC is provided by a number of observations. Although the direction of mean flow in the WGC is closely correlated with the 500 m isobath, recurvature to the west and south is noted at three primary locations. In Melville Bay the flow is observed to recurve southeastward around a shallow bank. A cross section of baroclinic velocities in this area not only indicates significant deep flow around the periphery of the bank, but confirms the filamental nature of the return current (Figure 4.3). The two distinct flow regimes on the southwest side of the bank are, as stated in Chapter 3, of different origins. Flow between Stations 128 and 129 is a recurved branch of the WGC which, assuming conservation of relative vorticity, probably forms a cyclonic gyre around the perimeter of the bank. Southwest of an apparent frontal boundary, however, a second axis of flow exists which has been shown to principally contain ABPW. Shoaling of the bottom in the vicinity of the Carey Islands causes complete recurvature of WGCAIW. The baroclinic velocity cross section from Jones Sound westward to Thule reveals that the core of the WGC is found east of Station 22 (Figure 4.4). Since water of Atlantic Laver origin has been confirmed between Stations 21 and 24. recurved flow of WGCAIW must pass between Stations 21 and 22. Calculation of baroclinic velocities between Stations 21 and 2 2. "i f h a of no motion assumed 62 STA. NO 131 130 z o cvi TJ c 0^ CQ > *4 1 a; T3 > 0/ — H ii 0/ 5 ~* to Ui U-I 3 •—4 O c; CL *— c o <U iH cs AJ w u to 0/ to 0/ > to —4 to to c to 1-1 a> o u V 3 u to 1—1 3 c 0/ a> 0/ 2 > a. •1-1 r- to —4 0/ »— 4 O c —A w u CC 0 jC. «— 4 L < > <L ci U- 63 from the geos trophic approximation, assuming a level of no motion at 200 dbars. Northward flow is indicated by positive isotachs, and southward i low by negative i so tachs . o •* w> *o _Z 0> 4J u z *Z J-4 ft <4/ Z 0 u 1-4 ft OH 0 •o l_l *z Z 2 * 5 0/ z O ON 0 4_y a> c •— 1 (—4 ct 00 C UH —H a ~h ■c u CO w-i z H-l o a: <L «-H ft 0 CO z Z ct CO w D CQ 00 CO ft -Cl •"5 *-H <L O X CO c £ JZ CO C3 <L c w Z O a 0 (L > m C*H U-i •1— 1 T 00 «-h 0 i-J H - ft u a> >■> O CO ■U -rH — • a> on « Z u <L i-j u tn C > U 0 Z i-H i— 4 *o •9-4 <L U 0; <L U u CO <L > 5 u z •iH U c CO — * 4J 4-J a CO ft a> u *z (L CO O E -O O <L r-H (L a a- v a u c *o co z r* <L O w CO - >-, H 'm Z •iH O' ft i-H > i— H •rH V - U-i u • 0 m z U *o o a> f— * Csl ~h 0 i z 5 (L Z <L -z >, 'w' P* Jt '_i Z r-. H ft ct <— — < ■o i-H U ft **H O r J> CsJ U ft CO Z 4- O fNI -H i-H r~ •*H DC JZ CO o —• t: co a. *-* cj ~ (L Z ft u 0 ft *~* o a bC ct u 5 4-J •— < rSj ft «~ *-> O z 00 -C co «r* ft a. ft Z - c o i-> < d ft 00 w vZ ft <r <L CC tZ 64 at 375 m, indicates that southward flow for this station pair is limited to the upper 55 in of the water column. Northward flow between Stations 22 and 23, calculated with a level of no motion at 400 in, decreased from 0.12 m/s at the surface to less than 0.03 m/s at a depth of 115 m. The implication of this result is that most baroclinici ty in the WGC is confined to the surface and near-surface layers. Barotropic currents are presumed to dominate below this level, hence, the postulated influence of topographic steering on the WGC. The remaining branch of the WGC is recurved at the northern extent of the 500 m isobath in Smith Sound. A meridional velocity cross section through the region further substantiates the classification of the baroclinic component of this flow as an ice edge jet (Figure 4.5). Baroclinic velocities between Stations 41 and 44, calculated with a level of no motion at 400 m, decreased from 0.44 m/s at the surface to approximately 0.04 m/s at 200 m. Below 200 m, predominantly barotropic flow is topographically steered to the west and south by rapid shoaling of the bottom. D. CIRCULATION IN NARES STRAIT The macroscale circulation regime in Nares Strait generates net southward flow of ABPW into Smith Sound. Mesoscale circulation patterns in the region, however, can not be characterized so succinctly. Inflow from the Lincoln Sea proceeds southward through Robeson and Kennedy Channels. A baroclinic velocity cross section through a southern part of Kennedy Channel indicates the relatively uniform nature of this flow (Figure 4.6). Recalling that southward Mow of NSAfW is terminated by rapid shoaling just north of this transect (refer to 65 66 Figure 6.5 A meridional baroclinlc velocity cross section from Baffin Bny northward to Kane Basin. Fositive isotarhs indicate flow to the west . W, STA. NO. 88 87 86 DISTANCE ( KM ) E Figure 4.6 A baroclinic velocity cross section through a southern part of Kennedy Channel. 67 Figure 3.19), it is probable that the relatively high current speeds in this area are associated with constriction of flow. Furthermore, shoaling is more extreme on the eastern side of the channel resulting in correspondingly higher speeds. In contrast, the high baroclinic current speed in Robeson Channel is probably due to the influence of the previously described local concentration of meltwater. Circulation in Kane Basin is characterized by southward flow in two peripheral branches, surrounding a central cyclonic gyre. Circulation along the eastern side of Kane Basin is topographically steered southward along the inherently shallow seabed. Augmented by runoff from the Humboldt Glacier, this eastern branch continues southwes tward and merges with recurved WGC water in Smith Sound. The flow of the western branch is also bathyme trically influenced. A portion of this branch turns cyclonically along the 200 m isobath forming a gyre, while the remainder continues southward, merging with both the western branch and the recurved WGC. The southern portion of the gyre is quite apparent in a baroclinic velocity cross section through Kane Basin (Figure 4.7). In contrast to its effect on the WGC, topographic steering does not appear to play as strong a role in Kane Basin. This implies that circulation within Kane Basin has a significant baroclinic component of flow. This presumption is most apparent between Stations 74 and 76, at the northern edge of the gyre. Baroclinic velocities between these stations reverse from southward at the surface, to northward below 65 in depth. This vertical shear in velocities is indicative of baroclinic instability, which might serve as a potential energy source for either the Kane Basin Gyre or smaller, undn t er f ^<1 *ddi«~s. 68 NW STA 69 Figure 4.7 A baroclinic velocity cross section through the southern portion of the Kane Basin Gyre. E. THE BAFFIN CURRENT The Baffin Current originates in Smith Sound, where southwest ward flow from Nares Strait merges with recurved WGC water. During its progression southward, the Baffin Current is augmented by outflows from Jones and Lancaster Sounds, and by WGC water which has recurved sou h of Smith Sound. As a typical western boundary current, the Baffin Current can be considered highly baroclinic. A baroclinic velocity profile between Stations 28 and 29, assuming a level of no motion at 400 m, indicates surface flow of 0.19 m/sec steadily decreasing to 0.5 m/sec at 200 m. Unlike the WGC, significant barocl inici ty in the Baffin Current is not coni ined to the upper 100 m. Interaction between the Coriolis force and bathymetry provides the primary steering influence for the Baffin Current. Throughout the course of the current, the tendency for westward turning by the Coriolis forte is offset by the presence of a lateral boundary. At the northern entrance to Jones and Lancaster Sounds, however, the removal of this restriction permits the observed westward intrusion of flow. It should be emphasized, however, that the barotropic component of flow associated with the Baffin current is not negligible. An examination of the baroclinic velocity cross section from Jones Sound eastward to Thule provides three clear cases of topographic steering (in conjunction with Figure 4.4, refer to Figure 4.1). Although a branch of the Baffin Current turns westward into Jones Sound, the main core of the current proceeds southward between Stations 18 and 1°. restricted bv 70 bathymetry. Also apparent are two cyclonic gyres; one around Coburg Island, and the other in the vicinity of a 150 m bank. Eastward outflow from the south side of Jones Sound subsequently merges with the main core of the Baffin Current along the coast of Devon Island. In contrast to the narrow filament entering Jones Sound, the major branch of the Baffin Current forms the westward intrusion of flow into Lancaster Sound. F. CIRCULATION IN THE SOUNDS 1 . Introduction Smith, Jones and Lancaster Sounds are all considered regions of net volume inflow to northern Baffin Bay. An examination of the circulation characteristics associated with each sound will provide a basis for their comparison. 2 . Smi th Sou nd Within Smith Sound exists a frontal boundary separating southward flowing ABPW and recurved WGC water. Circulation in this region, therefore, is determined primarily by baroclinic influences. A baroclinic velocity cross section through Smith Sound reveals a weak core between Stations 41 and 42 which is actually the remaining branch of the northward flowing WGC (Figure 4.8). Complete recurvature of this branch occurs just north of Station 41. Southward flow between Stations 42 and 43 is a filament of ABPW from the east branch of circulation in Kane Basin. The interaction between recurved BBSW and southwes twa rd flowing ABPW is marked by the presence oi a distinct ice edge. Indeed, the impingement of warm BBSW on the ire « dg* rrmtos a meltwater gradient which loccally elevates the dynamic heights, providing a strong 71 ON VIS O £ o o ( W ) Hid3Q o o CM 2 Id U 2 < cn o 72 Figure 6.8 A barocltnic velocity cross section through Smith Sound. baroclinic influence on flow direction. The resultant formation of an ice edge jet between Stations 40 and 41 marks the origin of the Baffin Current. Augmentation of the Baffin Current by ABPW occurs beneath the shallow pycnocline, which is associated with relatively warm, buoyant BBSW from the WGC (refer to Figure 3.4). Significant bathymetric influence in Smith Sound is limited to positioning of the frontal boundary between the two circulation regimes. Although topographic steering along the 500 m isobath clearly influences re< urvature of the WGC, baroclinic effects are responsible for the formation of the Baffin Current. Smith Sound, therefore, is the site where a significantly barotropic circulation regime is transformed into a predominantly baroclinic one. 3 . Jones Sound The combined influence of bathymetry and the Coriolis force on the circulation structure of Jones Sound is most apparent in a cross section of baroclinic velocities (Figure 4.9). A filament of the Baffin Current is deflected westward by the Coriolis force around the southeast corner of Ellesmere Island and into Jones Sound north of Station 15. Eastward outflow of ABPW is restricted to the south of Station 15, continuing along the east coast of Devon Island. The presence of a cyclonic gyre around Coburg Island (refer to Figure 4.1) links the flow paths accordingly. While eastward outflow from Jones Sound tends to follow the 500 m isobath, the westward intrusion is driven by the Coriolis force over a 200 m bank, against prevailing westerly winds. The baroclinic 73 Figure 4.9 A baroclinic velocity cross section through Jones Sound. 74 velocity cross section illustrates the relatively shallow nature of this westward intrusion of flow. 4. Lancaster Sound Circulation in Lancaster Sound is characterized by a westward intrusion of flow between Stations 6 and 8, and an eastward return current of greater magnitude between Stations 1 and 6 (Figure 4.10). The increase in velocities towards the sides of the sound indicates the effect of the Coriolis force on the inflow and outflow branches. Baroclinic velocities in the outflow branch are the highest in the entire NBB-NS region, reaching a maximum of 0.78 m/sec at the surface between Stations 2 and 3 (assuming a level of no motion at 340 m) . 5 . GeQ g tT.QB I nc Egtyigr in e Ci ircu iet j Qn Although their thermohaline and bathymetric features are inherently different, the general characteristics of circulation in Smith, Jones and Lancaster Sounds are remarkably similar. In each case, geos trophically balanced inflow is entrained, in estuarine fashion, by geos trophically balanced outflow. A quasi -vert ical frontal feature initially separates the two current regimes, the slope of which is determined by their respective velocity structures (refer, for example, to Figure 4.10). The dynamic aspects of the ensuing model, hereinafter referred to as Geostrophic Estuarine Circulation (GEC), are derived from the work of Leblond (1980). Variations in the observed character of the circulation in each sound can be explained in terms of how closely local conditions approximate GEC. In proposing a two layer ’’Coastal Current Model" to explain the observed circulation in some channels of the Canadian Archipelago. 75 ON VIS O CD Z m .O CD Z c (W) *Hld3Q “T O o OJ 2 J “m cm ro CM tO • « r * 'cm v> ^ ro p p ro — r- CD O O <0 o o CVJ O s~i 0 > u w cC y 5 aO D 0 aj u > u c u c • ^ T 3 S C .0 5 < CO a> u -j oL *i-4 U- 76 DISTANCE ( KM ) Leblond showed that two geostrophically balanced, upper-layer flows would coexist without interference in a channel whose width is sufficiently large compared to the local internal Rossby radius of deformation. Restriction of flow to the upper layer creates a sloped interfacial surface, resulting in a characteristically wedge-shaped velocity structure (Figure 4.11). I Figure 4.11 A schematic cross section of coastal upper layer flow (out of the page) of speed u, driven by a sea surface slope tj( y) The lower layer of density p 2 is at rest because the interface h(y) slopes in a direction opposite to that of the free surface. Y c is the distance from the coast at which the thickness of the upper layer vanishes (from Leblond, 1980, p. 191). Additionally, Leblond found that purely geostrophic flow can turn corners without separating from a coast if the radius of curvature of the coast is large enough that the Rossbv number remains well below unity. As a conservative estimate of the width of a coastal geostrophic current, V Q is defined as Y Q - R/F ; where R is the internal Rossby radius of deformation and F is the internal Froude number. If the width of a channel is shown to exceed 2 ( Y 0 ) , two geos trophical 1 v balanced upper-layer flows can theoretically exist without interference. 77 The results of applying L blond's equations to Smith, Jones and Lancaster Sounds are listed in Table II, with the requisite calculations presented in the Appendix. Since the computed Rossby number (R 0 ) at the mouths of all three sounds is less than 0.1, nonlinear effects may be locally neglected. It should be noted that values of Y Q are only calculated for the outflow regimes which, in each sound, were the widest of the two currents. Conditions in Lancaster Sound, with a minimum channel width (L) of 80 km, and a geostrophic cui rent width (Y Q ) of 20.35 km, most closely approximate GEC . Referring to the baroclinic velocity cross section through Lancaster Sound (Figure 4.10), it clear that although the calculated value of Y Q is considered an underestimation of the width of the outflow current, interference between the two circulation regimes appears negligible. The obvious wedge-shaped current structure implies that flow is primarily restricted to the upper 150 m. The broadening of the outflow wedge beyond the calculated value of V Q , however, indicates that this restriction is not complete. Indeed, the likelihood of significant flow occurring below 250 m depth is confirmed by the presence of WGCAIW in western Lancaster Sound. Entrainment of inflow results in cyclonic cross - channel flow. The connection of inflow and outflow currents in Lancaster Sound by cross-channel flow was most recently investigated by Fissel et al. (1982), who found the westward extent of the inflow intrusion strongly marked by dynamic height anomalies (Figure 4.12). This result illustrates that, in GEC, cyclonic cross - channel flow associated with entrainment of inflow is a geos trophica l 1 v balanced process. The 78 TABLE II GEOSTROPHIC ESTUARINE CIRCULATION MODEL CALCULATIONS CL) O -J E E E E 15 O O LD •»- T 3 00 L£> CO C 3 c 21 .c 0 *r- *0 _C -r- Q. 3 : E E E O — S- 4 -> 0 J* -*-> c >• 00 00 CO CD - — • • • O t- O 0 LD CD S- CJ 5 3 CO 00 CO O £ CO CO 0 Of CO E E E =3 ^ * 1 “ <T 3 “O LD 00 c <0 • • • V- a: a) +■> c M 00 r^ LD s- U CD •r~ X) 5 § cd :z CO E U_ CO CO •r- O) • • • co -a C 3 0 0 0 a> 0 Q s*. Ll. „ . O Od L£> CsJ CO U 0 O 0 CO CD • • • O jQ ad e 0 O 0 3 *0 c 3 O 00 -O -0 c c s- 3 3 CD 0 O CO 00 CO tv -C CO 0 CD c •I— c E 0 -J 00 -0 79 80 Figure 4.12 Surface dynamic height anomalies in eastern Lancaster Sound (in dynamic cm) relative to the 300 dbar level for four periods of CTD observations in 1979: (A) July 18-1 (B) July 29 - August 3; (C) September 2-4; and (D) September 14-23 (from Fissel et al . , 1982, p. 187). convergence of inflow and outflow regimes creates a local elevation in the sea surface, generating geos trophic flow normal to the resultant pressure gradient. With sufficient eastward outflow and the presence of lateral boundaries, characteristic cyclonic flow will result. Since convergence implies downwelling, a reduction in vertical density gradients may occur along this frontal feature, thereby enhancing the tendency for mixing. In Lancaster Sound the eastward outflow branch of the circulation illustrates the increase in volume and velocity typically associated with estuarine entrainment. In GEC, however, the entrainment is geostrophically , not turbulently, driven. The application of GEC to Smith Sound is influenced by both geometric constraints and significant horizontal density gradients. Referring to Table II, it is apparent that L is approximately equal to 2 (Y 0 ) . Since this is considered a minimum requirement, the potential for interference between the inflow and outflow regimes may be significant. This interference may manifest itself in the form of baroclinic instability and associated eddy generation. Within Smith Sound the inflow and outflow regimes are not appreciably influenced by coastal boundaries. The absence of a characteristically wedge-shaped velocity structure in this region is probably a consequence of this fact. Geostrophy does influence the direction of the inflow and outflow branches, however, resulting in cyclonic cross -channel flow. As stated previously, recurvature of the remaining branch of the WGC occurs as the result of an extreme horizontal density gradient at the ice-ed;;e Lront. Entrainment of WGC 81 inflow in Smith Sound, while not directly attributed to convergence, is nonetheless geos trophically balanced. The limitations in applying G EC to Jones Sound are considerable. Since L < 2(Y Q ), Jones Sound is wide enough to accommodate only one geos trophically-balanced current Referring to the 33.0 isohaline in Figure 3.14, the formation of densi y and, hence, baroclinic velocity wedges is evident at the sides of the channel; however, a complete blurring of the structure occurs between Stations 14 and 15. Since these current branches can not coexist in Jones Sound, it may be possible for complete intrusion of the westward inflow branch to occur at times, resulting in reversal of the net eastward flow in Jones Sound. Historical evidence of this occurrence has been cited by Muench (1971) (Figure 4.13). In 1962, for example, the flow is entirely westward, while in 1963 both inflow and outflow are present simultaneously but with the outflow dominant. The macroscale circulation pattern in the NBB-NS region can also be envisioned as conforming to the GEC model. Viewed simplistically , the inflowing waters of the WGC are geos trophical ly entrained at various latitudes, subsequently resulting in the augmented outflow which characterizes the Baffin Current. The predictably cyclonic circulation pattern associated with GEC is identifiable as a major macroscale feature in the region. G. BAROCLINIC TRANSPORTS Baroclinic transports derived from various arbitrary reference levels should be used, onlv with great reluctance, to infer continuity of volume. This is especially true in eastern boundary current regions, S2 0 / oD u. 83 Dynamic topography of the surface relative to 300 dbars in Jones Sound for various years; (from Muench, 1971, p. 92). like the WGC , where the baroclinici ty is known to be weak. The main purpose of this section, therefore, will be to qualitatively compare the baroclinic components of flow for major currents in the NBB-NS region. Unless otherwise specified, subsequent references to transports are summarized in plan view and assumed to be baroclinic in nature (Figure 4.14). The WGC achieves maximum transport in Melville Bay, prior to its previously described pattern of recurvature in northern Baffin Bay and Smith Sound. Transport of the WGC consequently decreases from a maximum of 0.7 Sv in Melville Bay, to 0.4 Sv in the vicinity of the Carey Islands, and 0.2 Sv in Smith Sound. The major portion of baroclinic transport is concentrated at the extreme inshore stations in Melville Bay, further substantiating the assumption that glacial runoff is primarily responsible for this component of WGC flow. The Baffin Current is partially derived from the net southward flow of Nares Strait. Southward transport increases from 0.2 Sv in Robeson Channel to 0.7 Sv at the mouth of Kennedy Channel. This increase may be attributed to admixture of meltwater runoff, in particular from Petermann's Glacier, located on the eastern shore of Robeson Channel. Southward transport through Kane Basin is primarily associated with the western circulation branch (0.3 Sv) , while southward transport in the eastern circulation branch is limited (0.1 Sv) . The swirl transport within the Kane Basin Gyre is approximately 0.4 Sv, indicative of its effect in recirculating meltwater from the Humboldt Glacier throughout the basin. The cyclonic ice-edge jet in Smith Sound, with associated transport of 0.5 Sv, can be considered as GEG outflow from Nares Strait 84 Figure 4.14 Major baroclinic transports in the NBB-NS region. 85 which is augmented by entrainment of the remainder of the WGC (0.2 Sv) . Net southward outflow from Kane Basin through Smith Sound, therefore, is inferred to be approximately 0.3 Sv. The Baffin Current, which becomes an identifiable feature in Smith Sound, continues southward along the coast of Ellesmere Island where transport is measured as 1.0 Sv . The formation of a topographically- induced cyclonic gyre is coincident with branching of the Baffin Currentnor theas t of Coburg Island. A westward flowing filament (0.1 Sv) enters Jones Sound, where it is entrained and augmented by eastward outflow (0.4 Sv) , resulting in net eastward transport of 0.3 Sv . A southwes tward flowing branch ( ).2 Sv) probably follows the 500 m isobath, subsequently merging with the main core of the Baffin Current. The relatively large transport (0.7 Sv) indicated southwest of Melville Bay is actually an algebraic summation of transports obtained between Stations 127 and 132 (refer to Figure 4.3). Southeastward transport of Baffin Current water (0.4 Sv) , probably derived from a branch of Lancaster Sound outflow which is topographically steered eastward along the 1000 m isobath (Muench, 1971), is apparent southwest of Station 130. Flow of WGC water, which has recurved either around the shallow bank in Melville Bay (0.2 Sv) or south of the Carey Islands (0.1 Sv) , is indicated between Stations 127 and 129. The main core of the Baffin Current, augmented by eastward outflow from Jones Sound, follows the southwest coast of Devon Island westward into Lancaster Sound (0.6 Sv) . GEC entrainment and subsequent augmentation of outflow yields gross eastward outflow of 1.7 Sv . Net 86 transport in Lancaster Sound, therefore, is inferred to be 1 . 1 Sv eastward . 87 V. THE NORTH WATER PROCESS The North Water Process is characterized by complex interaction between thermohaline and dynamic effects. The net result of this process is the demarcation of an 80,000 km 2 arctic region which is conspicuously devoid of first year ice from the onset of winter until March (Steffen and Ohmura . 1985). Following a brief examination of some relevant factors, a qualitative description of the process will be presented . In southern Baffin Bay freezing is generally accompanied by the formation of an isothermal isohaline near-surface layer approximately 75 m to 100 m in depth (Garrison et al . , 1976). Sea-ice production in the NBB-NS region is similarly associated with the formation of such deep mixed layers (Muench, 1971). In the weakly stratified waters of Nares Strait, convective processes are sufficient to form this homogenous layer. The region south of Smith Sound, however, is characterized by the ubiquitous occurrence of BBSW. The resultant presence of such a strong pycnocline would ordinarily limit the depth of convective mixing associated with surface freezing to much less than 75 m. A combination of turbulent and convective processes must be required, therefore, to overcome the inherent stability of this buoyant layer and produce the observed deep mixed layers. Given a particular set of climatic conditions, the enthalpy present in the near-surface layer determines the length of time required to initiate surface freezing. Assuming heat flux onlv through the surface and neglecting thermal advection, it is possible to evaluate this tiim* delay as a function of heat budget parameter-. St el ten and Ohmura 88 (1985) computed monthly and annual heat budgets for the North Water region and concluded, assuming a reference temperature of -1.8°C, that the amount of oceanic heat flux required to prevent ice formation is 337.4 MJM'2 i n October and 445.1 MJM'^ in November. The enthalpy contained in the 75-m deep, near-surface layer was calculated, referenced to -1.8°C, for all FRANKLIN 86 stations (Figure 5.1). For 22 stations located southward of Smith Sound, between 76° N and 78° N, the enthalpy in September averaged 475 MJ . Applying the aforementioned heat budget at the onset of winter (October), implies that surface freezing would be delayed by approximately five weeks in this region. In contrast, the average enthalpy contained in the ice -covered, near- surface layer north of 78°N (Nares Strait) was 120 M J . The presence of mechanical ice removal effects such as divergent currents and winds will cause the rate of sea-ice production to greatly exceed the rate of sea ice accumulation for a given area. This phenomena is graphically illustrated in the vicinity of the Kane Basil Gyre where cyclonic and, hence, divergent circulation results in an area of reduced ice concentration. Ice concentrations within the gyre were typically 3/10 or less, compared with surrounding concentrations of greater than 5/10. The cyclonic macroscale circulation pattern characteristic of northern Baffin Bay can be expected to provide a similar mitigating influence on the accumulation of sea- ice. The potential influence of persistent northerly winds on the reduction of sea-ice concentration in northern Baffin Bay has been discussed by Muench (1971) and Dunbar (1973). 89 Figure 5.1 Enthalpy of the near surface (upper 75 m) layer in the NBB-NS region (referenced to - 1 . 8 # C) . 90 The North Water Process results from the combined influences of near-surface layer enthalpy and mechanical ice removal. Since the North Water is characterized by reduced ice coverage, the associated decrease in albedo results in the largest annual net radiation for any region within the Arctic Circle (Steffen and Ohmura , 1985). Admixture of glacial runoff creates a strong, shallow pycnocline which effectively confines insolation effects to the near-surface layer. Such inherent stratification would normally restrict convective overturn associated with surface freezing to shallower depths. Mechanical ice removal, however, results in a proportionally greater rate of brine formation which increases the vertical extent of mixing. Complete removal of the enthalpy in this near surface layer delays significant sea-ice formation accordingly. Divergent cyclonic currents and northerly winds then serve to reduce sea -ice accumulation for the remainder of winter. It is the self-perpetuating nature of the North Water Process which accounts for its persistence. 91 vi. DISCUSSION The comprehensive nature of this analysis mandates further examination of certain relevant topics. A combination of elaboration and postulation will be employed in this regard. The dilution of WGC water masses, relative to those which enter the NBB-NS region through the Canadian Archipelago, is a consequence of the more extensive shelf-driven modification effects inherent in the former. The assertion by Muench (1971), that the major proportion of Arctic Ocean Water is less dense than Baffin Bay Water, was derived from point data sources, under the assumption that there are significant differences in water structures between the upper 250 m layers of the Arctic Ocean and Baffin Bay. Muench further concludes that these water- structure differences create a proportionally higher surface elevation in the Arctic Ocean, resulting in net southward transport. An examination of the dynamic topography of the NBB-NS region reveals an obvious lack of north-south dynamic height gradients (refer to Figure 4.2). This is due to the fact that ABPW and WGCPW have a common origin in the Arctic Basin, and are quite similar in thermohaline character. What is apparent, however, is a distinct dynamic height gradient normal to the coastline. Although the increase in dynamic heights in the onshore direction can be viewed as a consequence of the influence of the Coriolis force on the prevailing baroclinic flow, it may alternately be considered as a driving force for the observed circulation in the NBB-NS region. The ubiquitous glaciers in the region provide a significant coastal source of meltwater, an influence which mav he still ic lent to drive a 92 geos trophically -balanced current with the shoreline on the right, in the direction of flow. The implication of this hypothesis is that a progressive winter weakening in near-surface currents would be expected throughout the NBB-NS region. Lemon and Fissel (1982) provided evidence of just such an occurrence in northwestern Baffin Bay. On a larger scale, the concentration of glacial meltwater within the NBB-NS region results in near-surface layer dilution relative to the saltier waters of the North Atlantic. It is the difference in near- surface water structure between these regions that may drive the net southward baroclinic transport. A progressive winter decrease in this net southward transport would be expected accordingly. 93 vii. gfiacms^Ma The physical oceanography of the northern Baffin Bay - Nates Strait region has been investigated using a dense network of CTD stations occupied by the CCGS SIR JOHN FRANKLIN in September 1986. The following major conclusions can be drawn: * Five water masses can be delineated in the region. The WGC is the* source of WGCPW and WGCAIW, while ABPW and NSAIW are derived from the Arctic Basin via the Canadian Archipelago. WGCAIW and NSAIW are prevented by shoaling of the sea floor from entering Smith Sound and Kane Basin, respectively. BBSW is found seasonally throughout northern Baffin Bay. * The waters unique to the WGC are subject to more extensive dilution effects by shelf-driven processes and are comparatively less saline than their Canadian Archipelago derived counterparts. * Bathymetry provides a significant influence on the flow of the WGC, which attains a maximum baroclinic transport of 0.7 Sv in Melville Bay. Recurvature of component branches of the WGC occurs primarily in Melville Bay (0.2 Sv) , south of the Carey Islands (0.1 Sv), and ultimately in Smith Sound (0.2 Sv) . * The Baffin Current originates as an ice-edge jet in Smith Sound, subsequently proceeding southward along the coast of Ellesmere Island and throughout northwestern Baltin Bav. Transport ol the 94 Baffin Current is augmented by net outflow from Kane Basin, Jones Sound and Lancaster Sound at rates of 0.3 Sv, 0.3 Sv and 1.1 Sv, respectively . * Circulation in Smith, Jones and Lancaster Sounds can be described in terms of the GEC model, in which estuarine inflow, entrainment and outflow are geos trophically balanced processes. * Although a significant portion of the meltwater derived from the Humboldt Glacier is recirculated by the Kane Basin Gyre (0.4 Sv) , the influence of glacial admixture on thermohaline structure and near-surface circulation is apparent throughout the NBB-NS region * The North Water Process results from the combined influences of near-surface layer enthalpy and mechanical ice removal. 95 AEEEMDIX COMPUTATIONS ASSOCIATED WITH THE GEC MODEL The computation of geostrophic current widths in Smith, Jones and Lancaster Sounds is accomplished as prescribed by Leblond (1980). The requisite equations and calculations are presented here. The ’’Coastal Current Model" of Leblond (1980) assumes geostrophic flow confined to the upper layer of a two-layer stratified fluid, in a channel of width L and depth H (refer to Figure 4.11). Assuming the upper layer is relatively thin with respect to the lower layer, the speed of interfacial waves in the fluid may be approximated as: g(p2-p L ) t(o) (1) c = *1 where: g = the gravitational acceleration; Pi = the density of the upper layer; p 2 = the density of the lower layer; and t(o) = the thickness of the upper layer at the channel wall. In Smith Sound: pi *= 1025.5 kg/m 3 ; p 2 = 1027.0 kg/m 3 ; and t(o) * 75 m. In Jones Sound: pi ~ 1026.2 kg/m 3 ; p 2 = 1027.0 kg/m 3 ; and t(o) - 75 m. In Lancaster Sound: pi - 1026.0 kg/m 3 ; p 2 = 1027.0 kg/m 3 ; and t(o) - 150 m. The internal Rossby radius of deformation is defined as: R - C/f (2) where: f = the Coriolis parameter. The internal Froude number is defined as: % F - u/C (3) where: u « the speed of the upper layer flow. In Smith Sound: u - 0.25 m/s. In Jones Sound: u * 0.16 m/s. In Lancaster Sound: u * 0.50 m/s. The Rossby number is defined as: (4) where: r = the radius of curvature of the flow. In Smith Sound: r - 25 km. In Jones Sound: r * 75 km. In Lancaster Sound: r = 60 km. The width of the geostrophic current is then defined as: Y o (5) 97 LIST OF REFERENCES Aagaard, K. , and L.K. Coachman, The East Greenland Current north of the Denmark Strait, I, Arctic . 21, 181-200, 1968. Bourke, R.H., R.G. Paquette, and A.M. Weigel, MIZLANT 85 data report: results of an oceanographic cruise to the Greenland Sea, September, 1985, Tech. Rep. NPS 68-86-007, Dept, of Oceanography, Naval Postgraduate School, Monterey, California, 1986. Coachman, L.K. and K. Aagaard, Physical oceanography of Arctic and subarctic seas, in Arctic Geology and Oceanography , edited by Y. Herman, pp . 1-72, Springer- Verlag , New York, 1974. Dunbar, I.M., Winter regime of the North Water, Trans . R . Soc . Can . , 4(9), 275-281, 1973. Fissel, D.B., D.D. Lemon, and J.R. Birch, Major features of the summer near-surface circulation of western Baffin Bay, 1978 and 1979, Arctic . 35, 180-200, 1982. Garrison, G.R., H.R. Feldman and P. Becker, Oceanographic measurements in Baffin Bay, Unpublished manuscript. Applied Physics Laboratory, University of Washington, February, 1976. Leblond, P.H., On the surface circulation in some channels of the Canadian Arctic Archipelago, Arctic , 35, 189-197, 1980. Lemon, D.D. and D.B. Fissel, Seasonal variations in currents and water properties in northwestern Baffin Bay, 1978 and 1979, Arctic , 35, 211-218, 1982. Melling, H., R.A. Lake, D.R. Topham, and D.B. Fissel, Oceanic thermal structure in the western Canadian Arctic, Continental Shelf Research , 3, 233-258, 1984. Muench, R.D., The physical oceanography of the northern Baffin Bay region. Baffin Bay-North Water Pro j . Arct. Inst. North Am. Sci. Rep. , 1-72, 1971. Muench, R.D., and H.E. Sadler, Physical oceanographic observations in Baffin Bay and Davis Strait, Arctic , 26, 73-76, 1973. Sadler, H.E., Water, heat, and salt transports through Nares Strait, Ellesmere Island, J. Fish. Res. Board Can. . 33, 2286-2295, 1976. Steffen, K. and A. Ohmura , Heat exchange and surface conditions in the North Water, northern Baffin Bay, Ann . Glaciology . 6, 178-181. 1985. 98 Tunnicliffe, M.D., An investigation of the waters of the East Greenland Current, Master's Thesis, Naval Postgraduate School, Monterey, California, September 1985. 99 INITIAL DISTRIBUTION LIST No. Copies 1. Director Applied Physics Laboratory Attn: Mr. Robert E. Francois 1 Mr. E.A. Pence 1 Mr. G.R. Garrison 1 Library 1 University of Washington 1013 Northeast 40th Street Seattle, Washington 98105 2. Director 5 Arctic Submarine Laboratory Code 19, Building 371 Naval Ocean Systems Center San Diego, California 92152 3. Superintendent Naval Postgraduate School Attn: Dr. R.H. Bourke, Code 6RRf 7 Dr. R.G. Paquette, Code 68Pa 1 Dr. D.C. Smith IV, Code 68Si 1 Monterey, California 93943 4. Polar Research Laboratory, Inc. 1 6309 Carpinteria Ave. Carpinteria, California 93103 5. Chief of Naval Operations Department of the Navy Attn: N0P-02 1 NOP-22 1 N0P-964D2 1 N0P-095 1 N0P-098 1 Washington, District of Columbia 20350 6. Commander 1 Submarine Squadron THREE Fleet Station Post Office San Diego, California 92132 7. Commander 1 Submarine Group FIVE Fleet Station Post Office San Diego, California 92132 8. Dr. John L. Newton 1 10211 Rookwood Drive San Diego, California 92131 100 9. Director 1 Marine Physical Laboratory Scripps Institution of Oceanography San Diego, California 92132 10. Commanding Officer 1 Naval Intelligence Support Center 4301 Suitland Road Washington, District of Columbia 20390 11. Commander 1 Space and N< val Warfare Systems Command Department of the Navy Washington, District of Columbia 20360 12. Director 1 Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543 13. Commanding Officer 1 Naval Coastal Systems Laboratory Panama City, Florida 32401 14. Commanding Officer 1 Naval Submarine School Naval Submarine Base, New London Groton, Connecticut 06349-5700 15. Assistant Secretary of the Navy 1 (Research and Development) Department of the Navy Washington, District of Columbia 20350 16. Director of Defense Research and Engineering 1 Office of Assistant Director (Ocean Control) The Pentagon Washington, District of Columbia 20301 17. Commander, Naval Sea Systems Command 1 Department of the Navy Washington, District of Columbia 20362 18. Chief of Naval Research Department of the Navy Attn: Code 102-0S 1 Code 220 1 Code 1125 Arctic 1 800 N. Quincy Street Arlington, Virginia 22217 101 19. 1 Project Manager Anti-Submarine Warfare Systems Project Office (PM4) Department of the Navy Washington, District of Columbia 20360 20. Commanding Officer Naval Underwater Systems Center Newport, Rhode Island 02840 21. Commander Naval Air Systems Command Headquarters Department of the Navy Washington, District of Columbia 20361 22. Commander Naval Oceanographic Office Attn: Library Code 3330 Washington, District of Columbia 20373 23. Director Advanced Research Project Agency 1400 Wilson Boulevard Arlington, Virginia 22209 24. Commander SECOND Fleet Fleet Post Office New York, New York 09501 25. Commander THIRD Fleet Fleet Post Office San Francisco, California 96601 26. Commander Naval Surface Weapons Center White Oak Attn: Mr. M.M. Kleinerman Li brary Silver Springs, Maryland 20910 27. Officer-in-Charge New London Laboratory Naval Underwater Systems Center New London, Connecticut 06320 28. Commander Submarine Development Squadron TWELVE Naval Submarine Base New London Groton, Connecticut 06349 1 1 1 1 1 1 1 1 1 1 102 29. Commander Naval Weapons Center Attn: Library China Lake, California 93555 30. Commander Naval Electronics Laboratory Center Attn: Library 271 Catalina Boulevard San Diego, California 92152 31. Director Naval Research Laboratory Attn: Technical Information Division Washington, District of Columbia 20375 32. Director Ordnance Research Laboratory Pennsylvania State University State College, Pennsylvania 16801 33. Commander Submarine Force U.S. Atlantic Fleet Norfolk, Virginia 23511 34. Commander Submarine Force U.S. Pacific Fleet Attn: N- 2 1 Pearl Harbor, Hawaii 96860-6550 35. Commander Naval Air Development Center Warminster, Pennsylvania 18974 36. Commander Naval Ship Research and Development Center Bethesda, Maryland 20084 37. Commandant U.S. Coast Guard Headquarters 400 Seventh Street, S.W. Washington, District of Columbia 20590 38. Commander Pacific Area, U.S. Coast Guard 630 Sansome Street San Francisco, California 94126 39. Commander Atlantic Area, U.S. Coast Guard 159E, Navy Yard Annex Washington, District of Columbia 20590 1 1 1 1 1 1 1 1 1 1 1 103 1 40. Commanding Officer U.S. Coast Guard Oceanographic Unit Building 159E , Navy Yard Annex Washington, District of Columbia 20590 41. Scientific Liaison Office 1 Office of Naval Research Scripps Institute of Oceanography La Jolla, California 92037 42. Scripps Institution of Oceanography 1 Attn: Library P.0. Box 2367 La Jolla, California 92037 43. School of Oceanography University of Washington Attn: Dr. L.K. Coachman 1 Dr. S. Martin 1 Mr. D. Tripp 1 Library 1 Seattle, Washington 98195 44. School of Oceanography 1 Oregon State University Attn: Library Corvallis, Oregon 97331 45. CRREL U.S. Army Corps of Engineers Attn: Library 1 Hanover, New Hampshire 03755-1290 46. Commanding Officer 1 Fleet Numerical Oceanography Center Monterey, California 93943 47. Commanding Officer 1 Naval Environmental Prediction Research Facility Monterey, California 93943 48. Defense Technical Information Center 2 Cameron Station Alexandria, Virginia 22304-6145 49. Commander 1 Naval Oceanography Command NSTL Station Bay St. Louis, Mississippi 39529 104 50 . Commanding Officer Naval Ocean Research and Development Activity Attn: Technical Director NSTL Station Bay St. Louis, Mississippi 39529 51. Commanding Officer Naval Polar Oceanography Center, Suitland Washington, District of Columbia 20373 52. Director Nav^l Oceanography Division Naval Observatory 34th and Massachussetts Ave. NW Washington, District of Columbia 20390 53. Commanding Officer Naval Oceanographic Command NSTL Station Bay St. Louis, Mississippi 39522 54. Scott Polar Research Institute University of Cambridge Attn: Library Sea Ice Group Cambridge, ENGLAND CB2 1ER 55. Chairman Department of Oceanography U.S. Naval Academy Annapolis, Maryland 21402 56. Dr. James Mori son Polar Science Center 4057 Roosevelt Way, NE Seattle, Washington 98105 57. Dr. Kenneth Hunkins Lamont-Doherty Geological Observatory Palisades, New York 10964 58. Dr. David Paskowsky, Chief Oceanography Branch U.S. Department of the Coast Guard Research and Development Center Avery Point, Connecticut 06340 59. Science Applications, Inc. Attn: Dr. Robin Muench 13400B Northrup Way Suite 36 Bellevue, Washington 98005 1 1 1 1 1 1 2 1 1 1 1 105 1 60. Institute of Polar Studies Attn: Library 103 Mendenhal 1 125 South Oval Mall Columbus, Ohio 43210 61. Institute of Marine Science University of Alaska Attn: Library 1 Fairbanks, Alaska 99701 62. Department of Oceanography University of British Columbia Attn: Library 1 Vancouver, British Columbia CANADA V6T 1W5 63. Institute of Marine Science University of Alaska Attn: Dr. H.J. Niebauer 1 Fairbanks, Alaska 99701 64. Bedford Institute of Oceanography Attn: Dr. P. Jones 1 Library 1 P.0. Box 1006 Dartmouth, Nova Scotia CANADA B 2 / 4A2 65. Carol Pease 1 Pacific Marine Environmental Lab/NOAA 7600 Sand Point Way N.E. Seattle, Washington 98115 66. Department of Oceanography 1 Dalhousie University Hal i fax, Nova Scotia CANADA B3H 4J1 67. Dr. Richard Armstrong 2 MIZEX Data Manager National Snow and Ice Data Center Cooperative Institute for Research in Environmental Sciences Boulder, Colorado 80309 106 68. Institute of Ocean Sciences Attn: Dr. Eddy Carmack Dr. E. L. Lewis Dr. G. Holloway P.0. Box 6000 Sidney, British Columbia CANADA V8L 4B2 70. Dr. Knut Aagaard NOAA/PMEL NOAA Bldg. §3 7600 Sand Point Way, N.E. Seattle, Washington 98115 71. Department of Ocean Engineering Attn: Library Mass. Institute of Technology Cambridge, Massachusetts 02139 72. Dr. Theodore D. Foster Center for Coastal Marine Studies University of California Santa Cruz, California 95064 73. Research Administration Code 012 Naval Postgraduate School Monterey, California 93943-5000 74. Dr. Hugh D. Livingston Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543 75. Dr. T.0. Manley Lamont-Doherty Geological Observatory Palisades, New York 10964 76. Dr. A. Foldvik Geophysical Institute University of Bergen Bergen, NORWAY 77. Dr. Preben Gudmandsen Electromagnetics Institute Technical University of Denmark Building 349 DK-2800 Lyngby, DENMARK 78. Dr. D. Hanzlick Flow Industries, Inc. Kent, Washington 98064 107 1 1 1 1 1 1 1 1 1 1 1 1 I 79. Dr. W.D. Hibler Thayer School of Engineering Dartmouth College Hanover, New Hamsphire 03755 80. Director General Fleet Systems Attn: Ivan Cote' Canadian Coast Guard Tower A, Place de Ville Ottawa, Ontario Canada K1A 0N7 81. Mr. Tom Cocke Office of Marine Science U.S. Department of State Washington, D.C. 20525 82. Commanding Officer CCGS SIR JOHN FRANKLIN Canadian Coast Guard Base P.0. Box 1300 St. John's Newfoundland Canada A1C 6H8 83. M. Kim 0. McCoy SeaMetrics 9320 Chesapeake Dr. , #212 San Diego, CA 92123 84. CDR Erik Thomsen Danish Liaison Office Thule AFB Thule, Greenland 85. LT V. G. Addison, Jr. 46 Division Avenue Massapequa, N.Y. 11758 86. LT A.M. Weigel 4332 Great Oak Drive Charleston, SC 29418 87. Research Administration Code 012 Naval Postgraduate School Monterey, CA 93943-5000 88. Superintendent Naval Postgraduate School Attn: Library (Code 0142) Monterey, California 93943-5002 108 Thesis A24257 c. i Addison The physical oceano- graphy of the northern Baffin Bay-Nares Strait region.